Oxidation and Characterization of As‐Cast TRIP Steel Surfaces

Abstract

This paper presents recent results from a collaborative study between the Department of Ferrous Metallurgy at RWTH-Aachen University and the Department of Materials Science and Engineering at Carnegie Mellon University on high temperature oxide scale formation of AI and Si containing as cast TRIP steel surfaces under conditions similar to that of continuous casting and hot rolling. A combination of experimental studies consisting of (i) electron microprobe analysis and metallographic studies of the cast steel surface, (ii) direct visualization of the oxide formation through high temperature confocal scanning microscopy and (iii) Tammann furnace oxidation tests were carried out. It was found that internal oxidation of AI and Si takes place along the inter-dendritic boundaries, where AI and Si were found to have been enriched after casting. The scale formed on the steel surface was a complex mix1ure of solid fayalite ((FeO nl2(Si02 », wOstite (FeO n ), magnetite (Fe304), hematite (Fe203), and Fe-particulates and the rate of scale growth appears to have been controlled at high temperatures by the formation of a liquid slag layer that allows for rapid oxygen transport to the steel/scale interface.

In situ observations of early oxide formation in steel under hot‐rolling conditions

“…When thermo‐gravimetric techniques are applied to the study of oxidation, they are inherently limited to long‐term experiments and it is not possible to directly observe the progress of the oxidation process. Many attempts have been made to study oxide formation by in situ observations including the use of environmental scanning electron microscopy (Erhart et al , 1983; Lee & Rapp, 1988), high‐temperature laser‐scanning confocal microscopy (Senk et al , 2004; Thorning & Sridhar, 2005) and high‐temperature optical microscopy (Norton et al , 1993). The information that can be obtained through scanning electron microscopy is limited by the oxygen partial pressure that can be maintained in the specimen chamber without unduly affecting the vacuum and hence, the effective operation of the electron beam.…”

Effect of liquid phase on scale formation during high-temperature oxidation of AlSi-transformation-induced plasticity steel surfaces

“…Little work has been reported on oxidation during casting and hot rolling. It was recently shown, [9] from oxidation tests in a Tammann furnace, that there is evidence of a liquid phase that forms at 1200 °C, and there were indications that the existence of this phase could increase the rate of oxidation. In the case of low-carbon steels, a comprehensive review of the high-temperature oxidation of iron and steel in oxygen and air has been published.…”